Power from Plastics:Hopkins Scientists Create
All-polymer Battery

Researchers at The Johns Hopkins University have developed an
all-plastic battery, using polymers in place of the conventional
electrode materials. The battery, which is rechargeable and
environmentally friendly, has military and space applications and
may soon be suitable for small consumer devices, such as hearing
aids and wristwatches.

Popular
Science magazine honored the battery today with
a "Best of What's New" award, naming it one of
the top 100 new products, technology developments and scientific
achievements of 1996.

The Hopkins project was initiated and funded by
Rome Laboratory,
a U.S. Air Force research and development center in upstate New
York. Air Force officials asked Hopkins to create lightweight
plastic batteries that could be molded into almost any size and
shape for use in satellites and important military equipment.

Supervising the research at Hopkins were materials science and
engineering professors Theodore O. Poehler
and Peter C. Searson.
Along with researchers Jeffrey Killian, Hari Sarker and Jossef
Gofer, they have produced polymers that can generate up to 2.5
volts in cells that potentially could compete with the 3-volt
lithium batteries now on the market.
As part of this collaborative effort, engineers at Hopkins'
Applied Physics Laboratory, led by Joseph Suter, have been paving
the way for practical systems applications by linking the
batteries with an innovative solar cell charging system. They
also have contributed important technology and fabrication
know-how to the project.

Building an all-plastic cell was difficult because most polymers
that conduct electricity lack sufficient energy difference to
serve as electrodes. Batteries consist of three main components:
an anode (the positive electrode), a cathode (the negative one),
and an electrolyte (the conductive material between the
electrodes, such as the liquid in a car battery). Although other
researchers have used a polymer for one of these components,
Hopkins scientists are among the first to create a practical
battery in which both of the electrodes and the electrolyte are
made of polymers.

Lab tests indicate that the Hopkins cells can be recharged and
reused hundreds of times without degradation. Yet unlike nickel-
cadmium rechargeables, the all-polymer batteries contain no heavy
metals, which can contaminate soil and water. The polymer
batteries also contain no liquids, which can leak and pose safety
hazards.

The all-plastic battery operates efficiently in extreme heat or
cold. "A lot of battery materials vary with temperature," said
Poehler, who spearheaded the five-year research project. "For
example, your car battery doesn't start well when it's cold. But
you can cool the polymer battery much colder than you're ever
going to cool your car, and its properties don't change."

In addition, this power cell's unusual thin sandwich design makes
it highly adaptable. The anode and cathode are made of thin,
foil-like plastic sheets. The electrolyte is a polymer gel film
placed between the electrodes, holding the battery together. The
cell can be as thin as a business card, although a more power-
intensive application would require a larger unit. This thin,
flat design could allow battery users to cut a cell to fit a
specific space. "You can make it into whatever configuration you
want," said Searson. "You can imagine using it in a large sheet
form, so that you could have a battery that occupied an entire
wall, for example, but had very little thickness. Or you could
roll it up into a tube, like AA-size batteries."

These characteristics may be particularly useful in space
satellites, where polymer battery sheets could be slipped into
crevices without adding much extra weight, the researchers say.
If they were connected to solar cells, they could be recharged by
the sun's rays while the satellite is in orbit.

In recent months, the Hopkins researchers have applied for
patents and Fielded dozens of inquiries from battery
manufacturers who are considering mass production of the all-
polymer cells. "These batteries are very easy to make, and they
use simple stuff--organic compounds," Poehler said. "It's no more
complicated than what they're making now. The process is simple.
I don't see why they would cost any more money to make."

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